For bounded and unbounded domains in R 3 , we establish the lo- calization and the structure of the spectrum of normal vibrations described by systems of partial dieren tial equations modelling small displacements of com- pressible stratied uid in the homogeneous gravity eld. We also compare the spectral properties of gravitational and rotational operators. Our main result is the construction of Weyl sequence for the essential spectrum, which is an explicit form of non-uniqueness of the solutions.